Previous clinical research has described dietary fats and their role in modulating major species of plasma lipoproteins (Mensink et al. 2003; Am J Clin Nutr, 77:1146-1155), as well as their role in coronary heart disease and controlling plasma cholesterol levels (Steinberg et al. 1999; JAMA, 282(21): 2043-2050). Other research has studied changes in lipoprotein levels resulting from dietary fats that are rich in various fatty acids. For example, Tholstrup et al. (1994; Am J Clin Nutr, 59:371-377) studied changes in lipoprotein levels resulting from diets rich in different saturated fatty acids including stearic acid, palmitic acid, and lauric and myristic acids. Researchers have also studied and compared the abilities of different fatty acids to raise or lower overall cholesterol levels in human plasma. Most nutritional experts agree that saturated fatty acids as a class raise total cholesterol levels, while polyunsaturated fatty acids lower them. Monounsaturated fatty acids, e.g., oleic acid, are considered more neutral in their effect. It is also understood that the metabolism of individual fatty acid species within each class can impact HDL and LDL cholesterol levels to different degrees.
A number of research studies have suggested that, of all the more common saturated fatty acids, including lauric acid (C12:0), myristic acid (C14:0), palmitic acid (C16:0), and stearic acid (C18:0), it is myristic acid that is the most potent in elevating total cholesterol levels in plasma. Consistent with these findings, some manufacturers of processed foods avoid the use of hardening fats such as coconut oil or palm kernel oil, which contain high levels of myristic acid, in favor of palm stearin and regular palm oil, which are also hardening fats but contain high levels of palmitic and stearic acids instead.
A recently produced commercial margarine known as SMART BALANCE buttery spread (GFA Brands, Inc., Paramus, N.J.) combines the beneficial LDL cholesterol-lowering properties of polyunsaturated fatty acids, e.g., found in soybean oil, with the beneficial HDL cholesterol-raising and oil hardening properties of saturated fats. SMART BALANCE margarine incorporates regular palm oil which is rich in palmitic acid, rather than palm kernel oil which is rich in lauric and myristic acids, to achieve the requisite hardened texture. This margarine and related healthful fat blends are based upon the work of Sundram et al., and is described in U.S. Pat. Nos. 5,578,334, 5,843,497, 6,630,192 and 7,229,653, which are incorporated herein in their entireties. Sundram et al. describe a cholesterol-free blended fat composition that combines a polyunsaturated fat (15-40 wt % linoleic acid), and a cholesterol-free saturated fat in which the saturated fatty acids provide between 20% and 40% by weight of the composition. The effect of the saturated fat, i.e., palm oil, in this margarine is to increase both HDL and LDL cholesterol while the effect of the polyunsaturated vegetable oil is to lower LDL cholesterol. The net effect of periodically or regularly consuming such a fat blend composition instead of typical American dietary fat was shown to be a modest increase in the HDL concentration and an increase in the HDL/LDL concentration ratio in the blood.
Subfractions of palm oil, including palm stearin and so-called palm mid-fractions, have been commercially prepared without any chemical modification and used as hardstocks to solidify vegetable oils in margarines and table spreads. The palm stearins are differentiated from the mid-fractions in that stearins contain a high level of trisaturated triglycerides (e.g., tripalmitin or PPP) resulting in an elevated melting point (typically about 54° C.) whereas palm mid-fractions contain a significantly reduced level of PPP and an elevated level of disaturated triglycerides (e.g., POP containing two palmitates and one oleate fatty acid) resulting in a beneficially reduced melting point (about 32° C.). Commercial stearins and mid-fractions are available with fairly similar iodine values (IV level, a measure of the amount of unsaturation in fat; grams of iodine consumed by 100 grams of fat) that are compatible with margarine and shortening use (e.g., with medium IV levels of 30-35). The use of a similar IV level palm stearin and palm mid-fraction can provide similar texture or “softness” in the fat, suitable for margarine and shortening use.
Patents related to the use of palm mid-fraction in margarines and spreads include U.S. Pat. No. 4,115,598 (Moran), U.S. Pat. No. 4,388,339 (Lomneth), U.S. Pat. No. 4,390,561 (Blair), and U.S. Pat. No. 4,568,556 (McCoy). These patents describe the use of so-called palm mid-fractions as structural fats for solidifying vegetable oils such as soybean oil and sunflower oil. The functionally important solid fat content measured at room temperature for different preparations of palm mid-fraction can vary widely depending on the content of trisaturated, disaturated, and monosaturated triglycerides. Moran describes oil-in-water emulsions having 60% aqueous phase and 40% oil phase, in which the oil phase contains high levels of a palm mid-fraction (25%-30% by weight). However, such high levels of saturated fatty acids tend to elevate total cholesterol levels in human plasma. The palm mid-fraction of Moran is combined with either high levels of sunflower oil (70-75% by weight) or combined with partially hydrogenated (i.e., trans-fatty acid-containing) soybean and canola oils. The sunflower oil-rich fats of Moran contain very high levels of linoleic acid (49%-53%) which can undesirably depress HDL “good” cholesterol. Blair et al. describe margarine oils/fats prepared using about 35%-70% by weight of a palm mid-fraction structural fat. Their structural fat has a solid fat content (SFC or SFC value) that is low, i.e., less than 50% at room temperature (70° F.). Lomneth et al. describe a margarine (spreadable water-in-oil emulsion) in which an oil phase is prepared using a similarly elevated level (35%-70% by weight) of palm mid fraction structural fat with an SFC value between 31 and 58% at 70° F. Their structural fat is typically partially hydrogenated to decrease its iodine value to 39-50 from its higher natural IV value of approximately 48 and above. Using palm mid-fraction fats with lower SFC values requires that greater amounts of the palm mid-fraction be added to a vegetable oil to achieve hardening. However, these elevated levels of palm mid-fraction undesirably increase the cholesterolemic effect of the resulting fat blend. McCoy utilizes a palm mid-fraction fat that again has a low solid fat content (from about 31% to about 58% SFC at 70° F.). This low SFC necessitates the addition of a large amount of palm mid-fraction, about 35% to 70%, to solidify between 30% and 65% of the soft oil. Once again, using such elevated levels of palm mid-fraction hard fat contributes high levels of saturated fatty acids to a blended fat composition and is expected to raise plasma cholesterol levels when such table spreads are consumed as a nutritional fat on a regular basis.
Thus, there remains a need to develop margarines and table spreads that do not raise, and preferably which lower or more effectively lower, plasma cholesterol levels.